Stranded tungsten wire incandescent lamp filament

ABSTRACT

A TUNGSTEN WIRE INCANDESCENT LAMP FILAMENT IS DISCLOSED WHICH HAS A MUCH GREATER RESISTANCE TO FAILURE THEN ONVENTIONAL FILAMENTS, PARTICULARLY UNDER REPETITIVE SHOCK LOADS. THE IMPROVED FILAMENT IS MANUFACTURED BY SPIRALLY TWISTING A PLURALITY OF ROUND TUNGSTEN WIRES AROUND A ROUND CENTRAL TUGNSTEN WIRE AND DRAWING THROUGH A DIE TO REDUCE THE EFFECTIVE TRANSVERSE DIMENSION OF THE COMPOSITE TO FORM A COMPOSITE BODY HAVING A CIRCULAR CROSS-SECTION WITH THE CENTRAL STRAND HAVING A POLYGONAL CROSS-SECTION HAVING A PLURALITY OF PLANARSURFACE CORRESPONDING IN NUMBER TO THE OUTER STRANDS, THE OUTER STRANDS HAVING CORRESPONDING PLANAR SURFACES IN AREAL ENGAGEMENT WITH THE PLANAR SURFACES OF THE CENTRAL STRAND AND PLANAR SURFACES IN AREAL ENGAGEMENT WITH ADJOINING OUTER STRANDS.

March 23, 1971 J: WALTER ETAL 3,572,399

STRANDED TUNC'STEN WIRE INCANDESCENT LAM! FIL-AMENT Original Filed Aug. 5, 1966 dohn L.. Wot/tel",

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United States Patent 3,572,399 STRANDED TUNGSTEN WIRE INCANDESCENT LAMP FILAMENT John L. Walter, Scotia, N.Y., and Kenneth S. G. Pertwee,

South Euclid, Ohio, assignors to General Electric Comp y Original application Aug. 5, 1966, Ser. No. 570,602, now Patent No. 3,509,411. Divided and this application Nov. 29, 1968, Ser. No. 779,822

Int. Cl. B21f 7/00 U.S. Cl. 140-715 3 Claims ABSTRACT OF THE DISCLOSURE A tungsten wire incandescent lamp filament is disclosed which has a much greater resistance to failure than conventional filaments, particularly under repetitive shock loads. The improved filament is manufactured by spirally twisting a plurality of round tungsten wires around a round central tugnsten wire and drawing through a die to reduce the effective transverse dimension of the composite to form a composite body having a circular cross-section with the central strand having a polygonal cross-section having a plurality of planar surfaces corresponding in number to the outer strands, the outer strands having corresponding planar surfaces in areal engagement with the planar surfaces of the central strand and planar surfaces in areal engagement with adjoining outer strands.

STRANDED TUNGSTEN WIRE INCANDESCENT LAMP FILAMENT This is a divisional application of Ser. No. 570,602 filed on Aug. 5, 1966, now Pat. No. 3,509,411 and in the names of the present inventors bearing the same title and assigned to the assignee of the present application.

This invention relates to incandescent lamp filaments and more specifically to an improved multistrand tungsten filament having improved shock loading characteristics and to a lamp utilizing the improved filament.

It is well known that the history of the incandescent lamp, from its rudimentary beginnings and comparative inefiiciency to the present relatively efficient device, closely involves the filament. Many substances, both metallic and nonmetallic, have been tried as filament materials in the continuing effort to further improve lamp efiiciency and life. Gradually most incandescent lamps, setting aside those intended for special use, came to have tungsten filaments, since a comparatively high ratio of light output to power input was obtaintd and mechanical properties were also better than those of most available filament substances, particularly as the demands placed upon lamps by constantly expanding and advancing technologies increased. Lamps were called upon to do more than provide light under static conditions, they had to provide light reliably under severe operating conditions. For example, lamps used in automobiles and other ground transportation equipment must withstand shock loading conditions (vibration) while still delivering light for an acceptable service life. Even more stringent requirements must be fulfilled by lamps used in aircraft where vibration, particularly in some parts of the craft such as the tail and wing tips, can very drastically shorten the lamp service life. Needless to say, reliability in many of those situations is a premium requirement.

Since every year several billion electric lamps are produced throughout the world and the performance of these lamps depends mainly on the quality of the filament, there can be little speculation as to why improvement has been constantly sought in the tungsten filament. The brittle nature of tungsten results in manufacturing losses during coiling of the wire into the filament coil and the tendency for it to sag during lamp operation causes premature burnout. Sagging of the filament alters the distances between turns of the filament coil which in turn creates hot spots that ultimately result in coil burnout. Also, sagging alters the light emitting character of a lamp. Further, after a tungsten filament has been annealed, as occurs naturally as a result of lamp operation, it becomes even more brittle and susceptible to breakage. While the problems of sag and brittleness have been partially overcome by processing techniques such as using doped tungsten, they remain as problems significantly affecting lamp usefulness.

It is a principal object of this invention to provide a new filament wire for incandescent lamps which has improved ductility and shock resistance.

Another object of this invention is to provide a multistrand tungsten filament wire for incandescent lamps which has improved non-sag properties and increased strength and ductility under operating conditions where vibration exists during operation.

A further object of this invention is to provide an improved lamp utilizing the filament wire of this invention.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying specification and drawings.

FIG. 1 is a greatly enlarged photomicrograph of a cross-section of a filament wire according to this invention; and

FIG. 2 is an enlarged side elevation of a filament wire of the type shown sectioned in FIG. 1.

Broadly, the filament wire of this invention is a multistrand tungsten filament in which a single center strand is surrounded by a plurality of additional strands which spiral around it. The cross-section of the central strand is polygonal, the exact number of sides depending upon the number of strands spiraled around it. The outer or surrounding strands each have an arcuate outer surface and substantially planar side and inner surfaces that result in areal contact between adjoining outer strands and between each of the outer strands and the single center strand.

It was pointed out earlier that until the present time tungsten filaments for incandescent lamps were characteristically brittle in the annealed condition and have been subject to sagging, which reduces the service life. The problems arising from sagging have in the past been partially overcome by using tungsten doped with materials such as compounds containing aluminum, silicon and potassium. These doping materials cause the formation of a particular coarse, fibrous grain structure upon annealing heavily drawn wire containing them. Although doping alleviated the sagging problem somewhat, it nevertheless has remained a significant problem.

The present invention which provides increased filament ductility along with non-sagging characteristics has a unique multi-filament geometry previously unknown in the filament art. Specifically, referring to the FIG. 1 of the drawings, it can be seen that the filament wire 10 is comprised of seven individual strands and that there exists a single center strand 11 whose periphery is completely surrounded by the remaining outer strands 12, which are twisted around it as shown by FIG. 2. Further, it will be noted that between any two of adjoining outer strands 12 there exists planar contact as indicated at 15. Similarly,

a ratchet so as normally to prevent movement of the ratchet in the direction for releasing tension and the tension release means comprises an abutment on the sealing means which engages the holding pawl on movement of the sealing means away from the base and serves to release the holding pawl from its engagement with the ratchet.

4. A banding tool as claimed in claim 3 in which the abutment is a spring biased detent which yields on engagement with the holding pawl during movement of the sealing towards the base but, on engagement with the holding pawl during movement of the sealing means away from the base, resists displacement in order to disengage the holding pawl from its associated ratchet.

5. A banding tool as claimed in claim 3 in which the severing means is actuated by the tension release means.

6. A banding tool as claimed in claim 3 in which the holding pawl is pivoted with respect to the base and includes a toe portion extending away from the pivot and a raised portion disposed between the toe portion and the pivot, the toe portion being so constructed and arranged as to actuate the severing means after disengagement of the holding pawl from the ratchet and the raised portion being the part of the holding pawl to be engaged by the abutment.

7. A banding tool as claimed in claim 6 in which the severing means includes a cutter pivotally mounted with respect to the base adjacent to one end of the cutter and disposed transversely of the direction of the band over the base in a position such that part of the cutter spaced from the pivot lies within the locus of the toe portion and in which the cutter is biased by spring means so as to be urged against the toe portion and consequently that end of the holding pawl which is remote from the toe por tion is urged into contact with its associated ratchet.

8. A banding tool as claimed in claim 7 in which the abutment is a spring biased detent which yields on engagement with the holding pawl during movement of the sealing towards the base but, on engagement with the holding pawl during movement of the sealing means away from the base, resists displacement in order to disengage the holding pawl from its associated ratchet and in which the force due to the spring means urging the cutter into contact with the toe portion, the force due to the spring 'biasing the detent and the profile of the raised portion and that part of the detent which contacts the raised portion are so related that when the sealing means is moved towards the base no actuation of the severing means or tension release means occurs.

9. A banding tool as claimed in claim 1 in which the gripper means is biased to the open position and in use the free end of the band is inserted into the gripper in that position and the act of applying tension to the band establishes a driving connection between the band and the gripper so that the gripper moves to a positive locking position, the band being released automatically from the gripper when the tool is removed from the package.

10. A banding tool as claimed in claim 1 in which the tensioning means includes a manually-operable tensioning lever coupled by a drive pawl and associated ratchet to a capstan in which the band is held during tensioning and which is uni-directionally rotated upon actuation of the tensioning lever and in which the capstan is carried at one end of an axle journalled in the base and comprises at least one longitudinally-directed, open-ended slot which serves together with spring means associated with the slot to hold the band prior to the tensioning operation.

11. A banding tool as claimed in claim 10 in which the spring means comprises a leaf spring secured to the capstan and having a free portion extending obliquely across the slot and urged towards one side thereof.

12. A banding tool according to claim 1 in which the tensioning means includes a manually-operable tensioning lever coupled by a drive pawl and associated ratchet to a capstan in which the band is held during tensioning and which is uni-directionally rotated upon actuation of the tensioning lever and in which the drive pawl is urged by spring force into engagement with or towards the ratchet, and wherein the nose profile of the pawl and the spring force together predetermine the tension of the band in operation of the tool.

13. A banding tool as claimed in claim 12 in which adjustment of the spring force is provided and hence the final tension in the band can be varied.

14. A banding tool as claimed in claim 1 in which the tensioning means includes a manually-operable tensioning lever coupled by a drive pawl and associated ratchet to a capstan in which the band is held during tensioning and which is uni-directionally rotated upon actuation of the tensioning lever and in which the tensioning lever is spring biased towards a rest position and means are provided for withdrawing the drive pawl from the ratchet when the tensioning lever is in the rest position.

References Cited UNITED STATES PATENTS LOWELL A. LARSON, Primary Examiner US. Cl. X.R. l40--123.6 

